1. Field of the Invention
The present invention relates to the control of the amount of residual solvent in oat products and in particular to the control of the amount of residual solvent in comminuted oats that have been admixed with hydrocarbon solvent in a process for the separation of oil therefrom and/or in a process for the separation of fractions differing in protein content.
As used herein, the expression "groats" refers to the kernel of the oat, the expression "flour" refers to the endosperm of the oat, and the expression "bran" refers to the bran of the oat; such bran may have endosperm attached thereto. The expression "gum" refers in particular to water-soluble gum.
Oats are a potential source of a wide variety of useful products. Examples of such products are flour, starch, protein isolate and concentrate, proteinenriched flour, bran, gum and oil. Traditional techniques used in the cereal grain processing industry are frequently difficult to use with oats. For example, milling processes are difficult to use with oats because of process problems relating to the presence of oil in oats. Moreover, unless the oats are de-oiled prior to milling, such milling processes would result in the formation of flour and bran fractions containing oil which may result in the development of rancidity on the storage of the flour and bran.
2. Description of the Prior Art
Processes for the separation of comminuted oats into fractions, especially proteinaceous fractions, in which the comminuted oats or fractions thereof are admixed with hydrocarbon solvents for separation of the oil in the oats are known. Such processes are disclosed by R. W. Oughton in U.S. Pat. No. 4,208,259, issued June 17, 1980; U.S. Pat. Nos. 4,211,695 and 4,211,801, both issued July 8, 1980.
The use of hydrocarbon solvents, especially hexane, in order to de-oil proteinaceous materials containing oil, e.g., soya beans and cottonseed, is known. Moreover, in some countries the amount of residual solvent in the de-oiled material after separation from the oil bearing miscella, is subject to government regulation. For instance, under U.S. Food and Drug Administration Regulation No. 172,894, the amount of residual hexane in cottonseed meal for human use must be less than 60 ppm.
Several methods are known for reducing the amount of residual solvent in products that have been in contact with hydrocarbon solvents. For example, de-oiled soya beans have been treated with vacuum or steam or have been heated in ovens to promote evaporation of residual solvent. However, it has been found that even with intensive application of such methods, it is difficult to obtain products containing less than 60 ppm of residual solvent. Moreover, prolonged heating of proteinaceous products tends to result in denaturing of the protein.
A process for reducing the amount of residual solvent in soya beans is disclosed by W. G. Schultz in U.S. Pat. No. 3,966,981, which issued June 29, 1976. In that process, soya beans that contain residual hexane as a result of a de-oiling step are extracted with liquid carbon dioxide under conditions whereby the carbon dioxide remains in a liquid state. A process for the removal of residual solvent from proteinaceous materials, especially isopropanol from fish protein, by treating with air having a temperature of 40.degree.-90.degree. C. and at least 50% relative humidity, is disclosed in Canadian Patent 1,052,170 of T. Knutsen et al., which issued Apr. 10, 1979.
In spite of the methods known in the art, there is a need for an improved process for controlling the amount of residual solvent at a level of less than 60 ppm in products that have been in contact with hydrocarbon solvents.